A conventional battery charging system for charging battery power provided by a battery pack typically includes a voltage sense circuit, a current sense circuit, a loop filter, a pulse width modulation (PWM) circuit, and gate drive circuitry. The voltage sense circuit monitors the overall voltage provided by the battery pack, and the current sense circuit monitors a battery charging current across a current sense resistor. The voltage and current sense circuits provide an error deviation signal to the loop filter, which provides a filtered control signal to the PWM circuit. Using the filtered control signal, the PWM circuit generates PWM pulses for controlling the gate drive circuitry, thereby providing the battery charging current to the battery pack over a charging path.
The conventional battery charging system described herein has several drawbacks. For example, the voltage sense circuit typically monitors the overall voltage provided by the battery pack across terminals of the battery pack, where there can be a significant voltage drop. Such a voltage drop across the battery pack terminals not only can reduce the battery charging speed, but also can reduce the battery capacity. Further, during battery charging, a battery cell voltage can fail to reach a target level of the battery pack voltage. Because the capacity of the battery pack to store energy is generally dependent upon the battery cell voltage, the failure of the battery cell voltage to reach the target voltage level can further reduce the battery capacity. In addition, the charging path can have high impedance due to, e.g., the resistance of copper connections on a printed circuit board (PCB), connectors, switches, cables, etc. Such a high impedance of the charging path can reduce a fast charging period of battery charging, during which constant current charging is performed. Moreover, as temperatures rise, the resistance of the various elements in the charging path can increase, making the impedance of the charging path even higher, which can further reduce the battery charging speed, as well as the battery capacity.
It would therefore be desirable to have improved systems and methods of charging battery power that avoid at least some of the drawbacks of conventional battery charging systems.